A numerically controlled machine operating on the basis of X-Y Cartesian coordinates for cutting of glass sheets is disclosed in French Pat. No. 2,367,710. The machine is equipped with a carriage mounted at the intersection of two slides which form bridges between two coordinate guide bars, each slide being driven by a motor attached to the frame of the machine. Each motor drives a slide along one of the coordinate guide bars by means of a timing belt. The memory supplying the data of the cutting program comprises a magnetic tape on which the pulses controlling the driving motors are recorded, for example in the manner described in the publication of French Pat. No. 2,368,074. The magnetic tape can be replaced by the memory of a microcomputer.
This French patent also discloses using the cutting machine itself for recording the program on the magnetic tape by utilizing the cutting head of the carriage as a sensing head for guiding the carriage along a desired contour. In addition the patent discloses use of numerical pulse generators in the form of rotating devices which are placed directly on the shafts of the stationary motors.
If the Cartesian coordinate machine is used for producing the program, i.e. if the motion is transmitted by timing belts between the stationary motors and the sliding elements, an unavoidable stretching of the belts occurs such that slight tracing errors are introduced particularly if the dimensions of the machine are large. These errors may be a nuisance if cutting has to be done with very high precision.
In order to increase the precision of a cutting program, it is therefore desirable to create a separate recording device which is adapted to the specific parameters of the cutting machine to be used and which best meets the conditions required for the cutting of plate glass, particularly with respect to tracing precision.